This invention relates in general to antifriction bearings and more particularly to an antifriction bearing having improved lubricating capabilities for high speed operation.
Tapered roller bearings offer many advantages over other types of bearings, one of the more important being the ability to carry high thrust loads as well as high radial loads. The tapered design requires a thrust rib at the large end faces of the rollers to keep the rollers in position and alignment, the rib usually being a part of the cone or inner race. The nature of the contact between the rib and the roller end faces is such that a combination of rolling and sliding occurs, as opposed to the pure rolling contact between the roller side faces and the raceways. Due to this element of sliding at the rib-roller end contact, it becomes the critical area for lubrication, and the one where damage is most likely to initiate when lubrication is inadequate.
At low speeds, bearing rotation creates turbulence and churning of the lubricant which keeps all surfaces covered with adequate lubricant films. As speeds increase above about 5000 ft/min cone rib circumferential velocity, the centrifugal forces acting on the lubricant may tend to prevent lubricant from reaching the cone rib-roller end contact, thereby causing a starvation condition and allowing damage to initiate or occur.
Heretofore, various lubricating devices have been developed for in one way or another directing additional lubricating oil to the faces of the cone thrust ribs against which the large ends of the rollers bear in tapered roller bearings. While these devices enable the bearings to operate more satisfactorily at higher speeds, all have disadvantages of one type or another. For example, one way to improve the lubrication at the thrust rib is to provide the cone with oil holes or ports that extend axially through the rib to the face against which the rollers bear or perhaps radially through the cone to the rib face (see U.S. Pat. Nos. 3,811,743 and 2,217,801). The holes, however, must be accurately located, quite small, and placed at frequent intervals. They require additional machining operations which are very time consuming and may further complicate subsequent process steps such as heat treatments. Another approach is the curved oil dam located opposite the large diameter ends of the rollers. In this approach oil is pumped through the bearing in the normal manner by the tapered rollers, but instead flowing free of the bearing at the large end of the cup raceway, it is turned back inwardly by a curved dam so that it wets the large diameter ends of the rollers. The oil, however, is churned within the bearing and also absorbs heat from the regions of rolling contact along the raceways. It therefore is at an elevated temperature by the time it reaches the large ends of the rollers. Still another approach involves incorporating oil ducts or channels within the metal cage that maintains the correct spacing between the tapered rollers (see U.S. Pat. No. 3,628,835). The ducts or channels run along the cage bridges and convey the oil from the small end of the cage to the large end where they direct it against the large rib face of the cone. Metal cages of this nature are expensive to manufacture, and because of the clearances involved, it is difficult to position the discharge ends of the ducts close to the cone thrust rib. This could diminish the amount of lubrication reaching the cone thrust rib.